A Fatigue Damage Model for Failure Analysis of Single-lap Multi-bolt Joints

Abstract

As various kinds of composite connections are widely used in aircraft and space structures, the connection areas are generally the critical places in structures. In this article, the aim is to develop a damage model to study the fatigue behavior of fibrereinforced (FR) composite single-lap multi-bolt joints. In order to accurately simulate the fatigue evolution of composite bolted joints (CBJs), a user-defined three dimensional (3D) damage model was implemented in the commercial implicit finite element solver, ABAQUS, taking into account of material degradation and fatigue damage accumulation. S-N curves are calibrated against fatigue tests respectively in longitudinal, transverse and shear directions of laminates basing on Shokrieh’s empirical model which takes stress ratios into consideration. A two-parameter combined degradation model of the residual stiffness and residual strength is achieved from calibration of maximum stress ( max σ ) and fatigue life ratio ( n / N ). To accurately predict the stress-strain loops during each single cycle, a new intra-laminar exponential plasticity model including the coupling effects of shear and transverse stress responses is incorporated into present fatigue damage model, this plasticity model is capable to predict the nonlinear responses of shear and transverse stresses. Additionally, with the implementation of irreversible cyclic strain accumulation and Puck’s multi-axial failure criteria for the inter-fibre failure, the fatigue damage model successfully simulated the growth of hole elongation due to material degradation, bearing damage and unrecoverable deformation. Validation across a range of stress levels for single-lap CBJs indicates that the fatigue damage model proposed in this article is capable to predict the failure, fatigue life and damage evolution of single-lap CBJs.